One of the major human impacts that have affected the Sierra Nevada area is logging. The expanse of western civilization, was the reason for most of the heavy logging that drastically affected the area. Forest in the Sierra Nevada provided the lumber that humans required to expand cities. In fact, the Sacramento and San Joaquin Valleys were largely assisted in their foundation by the lumber obtained from this area. During this period lumber was used for transportation and growth of local markets. A great deal of the logging done was connected to the mining industry because timber was used to support the tunnels and prevent them from caving in. Most common method of logging in this area for a long period of time was clear-cutting which is a highly destructive form of logging and heavily impacted the forests of this area. In fact, once humans finally realized the negative impact such unsustainable clear cutting of forest was having, there was a move to start preserving the rapidly disappearing forests in the area. In 1890 Sequoia, Kings Canyon, and Yosemite National Parks were founded. Since then there has been a drop in the destruction logging had on this environment, in fact the future of these protected areas is decidedly more positive now that clear cutting has dropped and regulations have been enforced. In the last 90 years conifer forests have remained fairly consistent, and while there is no evidence that there is severe shrinking acreage, there have been no spreading acreage either.
This chart shows the increased area of protected forests in the Sierra Nevada.
The move from clear cutting to other means of logging, shows both the severity of the original impacts on forests and the move to preserve the present status of the protected forests in the Sierra Nevada, which attributes to the relative static status of the forests growth.
Above are some of the impacts humans have had on the forests in Sierra Nevada which explain their current status of relative unchanging status despite efforts to increase protection for these areas.
Sources:
McKelvey, Kevin, and James Johnston. "Historical Perspectives on Forests of the Sierra Nevada and
the Transverse Ranges of Southern California: Forest Conditions at the Turn of the Century." Trans.
Array USDA Forest Service Gen. Tech. Rep. PSW-GTR-133. 1992. 225-246. Print.
LinkWater
Forests are not the only aspect of the Sierra Nevada that has been affected by humans, the aquatic ecosystems in this area have also suffered. Of the watersheds in the Sierra Nevada 58% of the native aquatic biota are shown to be in poor or fair condition. Watersheds with particularly low scores are all located in the same areas that humans are using for agriculture, hydro-power, and hydraulic mining. While all these industries help provide the benefits of food and energy, needed for human civilization, the environmental impact, results in the deterioration of the regions watersheds, which then affect the animals in these habitats. In fact, many of the Sierra Nevada watersheds no longer have the native frogs and fish that used to originally populate them. The exploitation of logging, mining, trout stocking, and dam construction have all negatively impacted the water systems in the Sierra Nevada. The introduction of non native fish has also had a negative impact on the aquatic ecosystem. Actually, the three watersheds with the highest scores in relation to the W-IBI scores (Deer Creek, Mill Creek, Clavey River) all contain their native amphibian and fish and are in protected areas that allow for the continuation of a natural system that then preserves the water integrity for those areas.
"This dichotomy is reflected in the results of the principal components analysis, which produced two factors with eigenvalues greater than 1.00 (Table 1). Factor 1, explaining 42% of the variance, had only a moderate negative loading on the W-IBI score but was strongly positively loaded on the two road variables and strongly negatively loaded on mean elevation and the percentage of the watershed that was historically fishless. In factor 2, explaining 17% of the variance, the W-IBI score had a high negative loading, whereas the percentage of hectares containing dams, reservoir capacity, and the percentage of the watershed that was historically fishless had high positive loading" (Direct Quote).
Peter B. Moyle and Paul J. Randall, Evaluating the Biotic Integrity of Watersheds in the Sierra Nevada,
California. Wiley for Society for Conservation Biology. Conservation Biology, Vol. 12, No. 6 (Dec., 1998),
pp. 1318-1326.
LinkCalifornia. Wiley for Society for Conservation Biology. Conservation Biology, Vol. 12, No. 6 (Dec., 1998),
pp. 1318-1326.
Air
The air in the Sierra Nevada has also been affected by human civilization. The main reason for this being the California Central Valley air pollution, which is transferred from its original sites and is shown to spread deep into the Sierra Nevada area which is then able to negatively damage the protected areas in the Sierra Nevada. Studies show that this air pollution is indeed created by humans because the nitric acid and NH3 concentration levels diminish the farther away from human civilization (California Central Valley) one gets. The increased concentration of NH3 and HNO3 in the Sierra Nevada raises the N deposition amounts in forests in these areas elevating past levels that foster nutrition. This then affects the potential growth of forests, water quality, and animals exposed to this increase in the air pollutants. In this way, even the efforts to protect the forests and water systems in this area are hampered by civilizations toxic proximity to these areas.
"Calculated maximum and minimum dry N deposition from HNO3 and NH3 decreased eastwards. Sites closest to the San Joaquin Valley had the highest levels of HNO3 and NH3 deposition, with much lower N deposition resulting from HNO3 than from NH3" (Direct Quote).
Sources:
(http://www.sciencedirect.com/science/article/pii/S0269749110003179)
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